Known hydraulically-actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. Nos. 5,687,693 and 5,738,075 issued to Chen and Hafner et al. on Nov. 18, 1997 and Apr. 14, 1998, respectfully.
In these hydraulically actuated fuel injectors, a spring biased needle check opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high pressure actuation fluid, such as engine lubricating oil, when an actuator driven actuation fluid control valve, for example a solenoid driven actuation fluid control valve, opens the injector's high pressure inlet.
Injection is ended by operating the actuator to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the needle check to close under the action of its return spring and end injection.
A critical component of this type of hydraulically actuated fuel injector is the actuation fluid control valve, which admits the high pressure actuating fluid to the injector. Previous solenoid driven actuation fluid control valves can suffer a pressure capability problem because the solenoid force is often not strong enough to overcome very high actuating fluid pressures. Also, because the actuation fluid pressure in the high pressure actuation fluid supply rail is not absolutely constant, there may be a stability problem caused by fluctuating actuation fluid pressure, so that the timing at which the fuel injection starts and stops can vary.
Additionally, there is some inefficiency in the previous designs, especially those using poppet valves and the like, in that there is a very short period between when the valve is admitting high pressure actuation fluid to the injector, and when the valve is allowing the actuation fluid to drain from the injector, during which the passage that allows the actuation fluid to drain may be momentarily fluidly connected to the passage through which the high pressure actuation fluid is admitted. During this time, some hydraulic fluid (or rather, hydraulic fluid pressure) is wasted.
The invention is directed to addressing one or more of the problems set forth above.